1. FIELD OF THE INVENTION
The present invention relates to an apparatus for guiding, advancing, belaying, retracting or pushing an element of indeterminate length, such as webbing, rope, cable, chain, wire, etc., and more particularly to apparatus for such purpose employing an endless belt, chain, or other conveyance driven in a continuous geometric path around a support member such that the endless conveyance can travel in the continuous path without mobius twist.
2. BACKGROUND ART
Most of the existing traction devices for pushing, pulling or holding elongated elements with the advantage of force multiplication have many shortcomings. When the elongated element is stiff or contains glass fibers or instruments, existing capstan devices require a very large diameter drum to accommodate the element's minimum permissible bending radius. Should the element's outer covering be twist or wear sensitive, or should the surface finish be susceptive of deformation or degradation, as with towed streamers or fiber optic cable, the presently available capstan devices are of limited use because of the sliding that exists across the capstan drum face.
When the energy available to pull the elongated element is restricted, as in aircraft, spacecraft, watercraft, or robotic systems, most present capstan devices limit system function to accommodate capstan inefficiency. When the length to diameter aspect ratio is high due to installation restrictions, such as exist in aircraft, submarines and certain robotic installations, the presently available capstan devices far exceed the available space envelope.
One approach to this particular problem is set forth in my U.S. Pat. No. 4,274,574, which approached the problem of minimum bend radius and wear due to slippage at the drum, by utilizing a capstan inversion principle. The device taught in my prior patent, however, has a shortcoming of low belt life due to their mobius twist and a load induced longitudinal pendulum oscillation of the belts with a resultant helix angle change. This arrangement effectively causes a torsional stress on the elongated element. It is also quite difficult to manufacture the belts because of their mobius strip twisted construction. Functionally, such a mechanism is inefficient due to the multiplicity of pulleys, bearings and drive gears employed in the system and also presents rather low response time due to the inertia of the end plates, pulleys and gear assemblies employed. Earlier other devices employing somewhat similar techniques and also exhibiting similar problems are disclosed in U.S. Pat. Nos. 2,789,687 and 3,116,050.
Patents which recognize some of the problems recognized by the applicant, but nevertheless not exhibiting the satisfactory solutions that he has developed, include U.S. Pat. No. 4,343,422 which discloses a mechanical means of moving a web of material and deflecting the same at 90 degrees or 180 degrees. As taught by that patent a belt is employed to bend around two half tubes which are used to support rollers or balls. The belt slides then on its back surface on the outer cylinder and on its front surface on the inner surface. As disclosed, the belts employed in this patent teach the use of a back surface which may have grooves to help in maintaining its alignment. The grooves, however, are shown only on one side of the belt. Because of the nature of the design, a belt deflector or deflectors are employed to align the belt on the cylinder and elliptical shaped rollers and a groove of an exact dimension is employed to facilitate movement and overcome friction with a carrier belt employed to transport the carrier web.
A somewhat similar technique employing a single groove, single drum and single pulley device to provide accurate alignment of two finite length film strips through a relatively long path is disclosed in U.S. Pat. No. 2,561,497.